1. Field of the Invention
The present invention relates to a dynamic white balance control circuit and a multi-screen display device using the same, and more particularly to the dynamic white balance control circuit which can dynamically set a white balance and/or a color temperature of an image according to a signal level of an image signal and to a multi-screen display device using the dynamic white balance control circuit, and the multi-screen display device using the same.
The present application claims priority of Japanese Patent Application No. 2002-238109 filed on Aug. 19, 2002, which is hereby incorporated by reference.
2. Description of the Related Art
Conventionally, various technologies of a white balance control circuit adapted to calibrate a white balance and/or a color temperature of an image are known. As various kinds of conventional devices used to control the white balance control circuit for an image signal, there are provided an image data judging device to judge whether or not a dominant color exists on a screen by converting sampled image data to chromaticity signals and luminance signals and by counting the chromaticity signals in a limited region for processing, a color chart recognizing device to identify a color chart image by checking distribution of the chromaticity signals using a statistical amount calculating section, a light source presuming device to presume a light source by processing an iris calibrating mechanism control signal to judge whether or not light from an outside has been applied, and a like, as disclosed in, for example, Japanese Patent Application Laid-open No. Hei 6-70345 (here, this technology is called a “first conventional technology”).
Moreover, in an image pickup device such as a video camera, electronic still camera, or a like, in order to improve accuracy that can be improved when a white region is small and to be able to calibrate a white balance even when a white region is large, an idea has been proposed. That is, after having divided an input image into a plurality of blocks using a block data detecting circuit, the image data is detected for every block. Then, a block being a white region is selected using a white region selecting circuit. If the number of blocks judged to have been a white region becomes large, by making small a width for judging convergence among color signals used to judge whether or not white balance calibration has converged using a white balance convergence judging width determining circuit and by detecting a level of each color signal using a white region image data detecting circuit, the white balance is calibrated using the white balance control circuit so that each color signal has a width indicating that the white balance calibration is judged to have converged, as disclosed in Japanese Patent Application Laid-open No. 2001-169307 (here, this technology is called a second conventional technology).
Also, in order to prevent a coloring phenomenon from occurring when a black and white image is input by making a white balance correction for an image display device, another idea has been proposed. That is, color image correction characteristic data obtained by a gamma correction and a white balance correction for every red, green, and blue image data is stored in advance in a memory section and a burst signal detecting section to detect a color burst signal from an original composite image signal is provided. Then, when the color burst signal is detected, a plurality of image converting sections each corresponding to each image data performs an input/output level conversion based on color image correction characteristic data. When the color burst signal is not detected, a control section exerts control on the memory section and on each of the image converting sections so that an input/output level conversion is performed based on predetermined color correction characteristic data selected from the color image correction characteristic data, as disclosed in, for example, Japanese Patent Application Laid-open No. Hei 11-205813 (here, this technology is called a third conventional technology).
Furthermore, in order to achieve gray scale and white balance calibration that can obtain a high hue and a high contrast in black display of an image, a correction data producing method for an image display device is known, which includes a step of storing chromaticity measured data, a step of storing luminance characteristic measured data, a step of setting and storing white display targeted chromaticity, a step of calculating a white display composite luminance ratio, a step of calculating corrected maximum luminance of each of red, green, and blue colors, a step of setting and storing black display targeted chromaticity, a step of calculating a black display composite luminance ratio, a step of calculating corrected minimum luminance of each of red, green, and blue colors from the black display composite luminance ratio and the luminance characteristic measured data, a step of producing a targeted luminance function from a gray level function representing a gray shade of luminance obtained after correction and from the corrected maximum luminance and corrected minimum luminance, a step of producing a luminance characteristic function from luminance characteristic measured data, and a step of calculating correction data from the targeted luminance function and luminance characteristic function, as disclosed in, for example, Japanese Patent Application Laid-open No. Hei 11-355798 (here, this technology is called a fourth conventional technology).
In the first conventional technology described above, the method is proposed in which the white balance control circuit in an image pickup device can calibrate the white balance irrespective of the size of the area in the white region in the screen. Moreover, in the second conventional technology, the method is proposed in which the white balance control circuit in the image pickup device can calibrate the white balance irrespective of influences caused by external light (from a light source). Also, in the third conventional technology, the method is proposed in which occurrence of coloring phenomenon can be prevented in the black and white image in which, at the time of inputting the black and white image, coloring occurs in the screen display depending on characteristics of the display device. Furthermore, in the fourth conventional technology, the method is proposed, in the image display device, a hue in black can be improved while a decrease in contrast can be suppressed.
However, such the conventional technologies have a problem. That is, in each of the conventional white balance control circuits, since a white balance and/or a color temperature are set by using, as a reference, a black and white image region in a screen, a tint (for example, a flesh color) of a colored image region in the screen becomes worse, or if the white balance and/or the color temperature are set by using as a reference, the colored image region, the color temperature becomes too low.